Estes Semi-Scale Saturn V, Kit #K-39, Part 8, Prepping The Tunnel Dowels

The back side of the WD-2 dowels need to be sanded flat to glue onto the body tube. This can be difficult, the dowel will want to roll.

Mark a straight line down the length of the dowel using the side of the pencil point. Facing up, this will be your straight line reference as you sand off then re-draw the pencil line until the dowel length is half.

Using 220 grit on a block - 

As you sand back and forth, the pencil line will be removed. Remark the line and continue to sand until you have a crescent half circle.

TIP: It's easier to sand from the mid point to the end. Redraw the pencil line. Flip the dowel (still pencil line up) and sand the pencil line on the other side.

Here's the before and after. 

This operation is tricky - the dowel is only 1/12" diameter.